• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1720-1730
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• 1995

Finite-difference analysis was conducted to study the natural convection of a stably stratified salt-water solution in an annulus due to lateral heating. The main purpose of this study is to examine in detail the multi-layered flow structure. Calculation was thus made for R $a_{\eta}$=2*10$^{5}$ and 6.5*10$^{5}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nusselt number variations with time are examined. Numerical results show that in each layer, the temperature profile looks 'S`-shaped and the concentration profile is uniform due to the convective mixing. The formation of the roll and the layer is governed by natural convection due to the temperature gradient and the merging process of the layer by diffusion of the concentration.ation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1422-1436
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• 1997

Numerical investigations were conducted to study the convective phenomena of an initially stably stratified salt water solution with lateral heating in a uniformly rotating annulus. The method of investigation is the finite difference analysis of the basic conservation equation for an axisymmetric, unsteady, double-diffusive convection and calculation is made for R $a_{\eta}$=2*10$^{5}$ and Ta=10$^{7}$ ~ 2.5*10$^{8}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nu variation with time are examined. Numerical results show that in each layer, the temperature profile looks 'S'-shaped and the concentration profile is uniform due to the convective mixing. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly. As the effect of the rotation increases, the generation of rolls at hot wall, the formation and merging of layers are delayed. The average Nu shows the trend of conduction heat transferees the effect of the rotation increases.n increases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.222-227
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• 2020

Pb(Zr,Ti)O₃(denoted as PZT) in the perovskite phase is used as a dielectric, piezoelectric, and super appetizer material owing to its ferroelectric properties. A PZT film was formed by an RF magnetron sputtering process by preparing a target composed of Pb_1.3(Zr_0.52Ti_0.48)O₃. The PZT film was formed by dividing the material into a mono-layer PZT produced continuously with the same sputtering power and a bi-layer PZT produced with two-stage sputtering power. The bi-layer PZT consisted of a lower layer produced under low-power sputtering conditions and an upper layer produced under the same conditions as the mono-layer PZT. XRD revealed small amounts of pyrochlore phase in the mono-layer PZT, but only the perovskite phase was detected in the bi-layer PZT. SEM and AFM revealed the upper part of the bi-layer PZT to be more compact and smooth. Moreover, the bi-layered PZT showed superior symmetry polarization and a significantly reduced leakage current of less than 1×10-5 A/cm². This phenomenon observed in bi-layer PZT was attributed to the induction of growth into a pure perovskite phase by suppressing the formation of a pyrochlore phase in the upper PZT layer where the densely formed lower PZT layer was produced sequentially.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.415-425
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• 2016

Load-bearing steel stud wall system is widely used for the middle-to-high rise modular buildings worldwide. Seismic performance is a key issue to apply load-bearing steel stud wall system to modular buildings in Korea. This study proposes a new strap braced steel stud wall system with enhanced seismic performance and design equations considering the flexural behaviour of the vertical outer studs. For the verification, two specimens with different strap braces and vertical outer stud were designed and tested. The test results showed that the total strengths were evaluated to be 1.11 to 1.18 times higher than the predicted values. Usually strap braced walls are considered to have low energy dissipation capacities. The proposed system showed enhanced seismic performance with equivalent damping of 9.42% due to the reduced pinching effects.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1709-1719
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• 1995

The primary objective of the paper is to obtain the basic information of the natural convection of a stratified with various parametric conditions related to rotating speed, temperature and concentration gradient. For the purpose of it, experiments are performed in a stably stratified salt-water solution with lateral heating in a stationary or rotating annulus. The experiment covers the ranges of Ar=2, Le=100, R $a_{\ta}$=2 10$^{5}$ and Ta=0, 10$^{5}$ - 2.5*10$^{8}$ . Many interesting flow phenomena are observed and rotation effects are examined. Particularly as Taylor number increases (rotation increases) at a given R $a_{\ta}$, the generation of rolls at hot wall is inhibited and the formation and merging process of layers are delayed.

• Elastomers and Composites
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• v.43 no.2
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• pp.82-87
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• 2008

In this study, nine kinds of polyimides were synthesized from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA), m-pheny lenediamine (m-PDA) and 4,4'-oxydianiline (ODA) by controlling molar ratio of monomers. Synthesized polyimides were used as insulator films for 2-layer Flexible Copper Clad Laminate(FCCL) which were manufactured by the casting method. Glass transition temperature and thermal degradation temperature for 5% weight loss of the polyimide film were improved by increasing contents of m-PDA and PMDA, respectively. Water absorption of polyimide film was reduced by increasing contents of ODA and BPADA which have relatively long structure, respectively. Peel strength of 2-layer FCCL was improved by increasing contents of ODA and BPADA.

• Resources Recycling
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• v.24 no.5
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• pp.3-14
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• 2015

This study investigated that status of domestic and international furnace desulfurization and desulfurization characteristics of limestone for fluidized bed use depending on the technology for CFBC one of the CCPs. Limestone-based desulfurizing agent is one of the superior elements which are optimal at around $850-950^{\circ}C$ on high temperature desulfurization. And effectiveness of desulfurization process can be determined by the desulfurization experiment method such as diffusion reaction of the diaphragm of the absorber surface, the size of the particles, the pores of the quantity, size and structure. And, desulfurization efficiency depending on geological and crystallographic properties and calcination process of limestone needs additional research in the future.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.72-77
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• 2001

Top spin valve films with PtMn antiferromagnetic layers were deposited using a multi-target dc magnetron sputtering in (100)Si substrates overcoated with 500 $\AA$ of Al$_2$O$_3$. Firstly, the post-deposition annealing was performed at 270$\^{C}$ in a unidirectional magnetic field of 3 kOe to induce the crystallographic transformation of the PtMn layer from a fcc (111) to a fct (111) structure. Secondly, the spin valve films were annealed without magnetic fields and magnetic properties were measured. In Si/A1$_2$O$_3$ (500$\AA$)/Ta(50$\AA$)NiFe(40$\AA$)/CoFe(17$\AA$)/Cu(28$\AA$)/CoFe (30$\AA$)PtMn(200$\AA$)Ta(50$\AA$) top spin valve samples, the MR ratio decreased slowly with increasing annealing temperature up to 325$\^{C}$. But above 325$\^{C}$, the MR ratio decreased rapidly to 1%, due to a collapse of the exchange coupling between a antiferromagnetic layer and a pinned layer with increasing annealing temperature. Also above 325$\^{C}$, the exchange biased field rapidly decreased and the interlayer coupling field rapidly increased with increasing annealing temperature. A change in the interlayer coupling field was resulted from the increase in interface roughness due to Mn-interdiffusion through the grain boundaries. We confirmed the temperature in changing magnetic properties agreed well with the blocking temperature of PtMn based spin valve structure.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.17-26
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• 2016

The experimental investigation aims at developing controlled low strength materials (CLSM) using a self-cementitious fly ash (FA) as a binder and a bottom ash (BA) as a aggregate. The fly ash and bottom ash used in this study were obtained from a circulating fluidized bed combustion boiler (CFBC) which produces relatively high CaO containing fly ash. To find the optimum mixing condition satisfying flow consistency and unconfined compression strength (UCS), the CLSM specimens were prepared under various mixing conditions, including two types of aggregate and different weight fractions between fly ash and aggregate. Additionally, the prepared specimens were evaluated using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The results of this study demonstrate that the water content satisfying flow consistency ranges from 42% to 85% and the flowability is improved with increasing the fraction of aggregate in whole mixture. The USC ranges from 0.3 MPa to 1.9 MPa. The results of UCS increases with increasing the fraction of aggregate in FA-sand mixtures, but decreases with increasing the fraction of aggregate in FA-BA mixtures. SEM images and XRD patterns reveal that the occurrence of both geopolymerization and hydration. The results of this study demonstrate that CFBC fly ash could be used as an alternative binder of CLSM mixtures.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.54-63
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• 2007

The sedimentary sequence of the non-marine Cretaceous Jinju Formation from Sacheon, Korea, contains a number of rod-shaped stromatolites (RSS) characterized by concentric lamination with curd-shaped, stratiform, and small columnar stromatolites. Unlike the world trend, a massive distribution of rod-shaped stomatolite was discovered in the region. The mineral composition, diagenetic alteration, and weathering process of the kind were analyzed by EPMA. The gross morphology of RSS is almost identical to broken plant twigs or stems formed by microbial activity onto which it grew. RSSs are interpreted as stromatolitic algae over plant twigs, which formed through concentric carbonate precipitation by epiphytic algal photosynthesis. The distribution of localities and horizons of the stromatolite imply that RSS is allochthonous and autochthonous. Two types of cyanobacterial filaments and one type of peen algal filament were discovered. The size frequency distribution of calcified filamentous microfossils found in stromatolite was $2.2{\mu}m\;and\;7.8{\mu}m$ in mean diameter of the former, $32.3{\mu}m$ in mean diameter of the latter. The cyanobacterial fossils played a key role in the formation of stromatolite, while the green algal filament was auxiliary stromatolite-builder stromatolites. The filamentous microfossils including trichome were found within the stromatolitic laminae.